Soil erosion from cropland is affected by the areal fraction of the land surface covered by crop residue, the non-living portion of a crop left in the field after harvest. Management of crop residues requires leaving a substantial amount of such residues in place in order to minimize soil erosion. As little as 30% coverage of the soil by residue can reduce soil erosion by approximately 90%. Proper crop residue management constitutes an important soil and water conservation measure and federal law requires the Chief of the Soil Conservation Service to maintain technical standards and criteria to assure that practices employed meet intended purposes. In order to manage such residues intelligently, a rapid, accurate, and objective measurement of the amount of crop residue cover on agricultural land is needed.
Two basic methods are currently employed for measuring crop residue: the photographic and intercept techniques. They are statistical in nature, require multiple assessments, and are also, to some degree, subjective.
The photographic technique consists of taking single down-looking photographs or stereographic pairs of photographs of residue and soil and thereafter manually estimating the fraction of the soil covered by residue from the photographs. Video cameras and computer-aided analysis of the video images of reflected visible light provide enhancements to the photographic technique.
The intercept techniques may be grouped into line-transect and point-intercept methods. With the line-transect method, measurements of crop residue cover are made along the length of a line across the field and average residue cover determined statistically. The point-intercept method uses a system of cross-hairs, grid points, or dot matrices to define points where the presence or absence of residue is determined. At present, the line-transect and point-intercept methods are the most popular methods used to estimate crop residue cover and many variations of these methods have been reported. Sometimes line-transect and point-intercept methods are combined, e.g., a line is placed and the intercept is read at selected points. Accuracy of this line-point transect depends on the length of the line and the number of points used per line.
The disadvantages of the photographic reflected visible light technique are the very slow analysis of the photographs in the laboratory and the special equipment required. Furthermore, there is typically a delay of several days from the date of observation until the analysis is completed. This delay may not be acceptable for making decisions regarding residue management.
Although the line-intercept and point-intercept methods and a combination thereof are deemed to be as accurate as the photographic method, they are slow, tedious, and somewhat subjective. There is a need for a method and apparatus which will overcome these disadvantages. This invention will provide the advantages of rapid, accurate, and objective measurement of crop residue cover to an extent unavailable using current methods and devices, and will provide the added advantage of a readily transportable measurement apparatus.
An additional advantage of this invention is its capability to detect live vegetation, as well as most dead organic matter and to distinguish these from most soils and, further, to measure the rate of decay of the dead organic material covering the soil. The method of this invention will thus be applicable in the field of land assessment, providing a measure of ground cover by organic material and of stress or damage to the vegetative cover.